Tuesday, 12 July 2011

Mealtime and Weight Loss

More in the AM? Maybe not!

In order to lose weight, it is important eat more in the morning and less in the evening, right?  Wrong!  Well, the answer may be a little more complicated than that, but a study I recently came across published in the Journal of Nutrition suggests consuming more at night may have some very important benefits that should not be ignored.

Firstly, I should point out that everything you know about eating in the morning is not unfounded.  Two studies discussed in the paper referenced below prove that weight loss occurs when a single meal is consumed in the morning, whereas weight gain occurs when that same meal is consumed in the evening.  Common sense suggests that if you ingest food in the morning, your body utilizes those calories throughout the day before they have the chance to be stored (partially in fat).  On the other hand, the food you eat at night is readily stored, providing an increased opportunity for fat formation.

This makes sense to me, which is why I was so surprised when I came across this study.  Why would night-time meals be beneficial?  The answer comes down to how your food is stored, and how you access these stores for energy.

How is my Food Stored?

The process of food digestion, storage and subsequent release for energy is fairly complicated.  Yet, when you partake in aerobic exercise, the main source of energy is from two places- fat and muscle glycogen.  

When you eat a cookie, for example, your body digests and breaks down this carbohydrate rich grub into individual sugar molecules- glucose:

The infamous glucose molecule

The first job that glucose fulfills is to fuel your energy needs in that very moment.  So, if you are going for a jog, much of the glucose will be converted directly into energy to help you complete that run.  The unused glucose is then packed into long chains and is stored in your muscles.  These chains of glucose are called glycogen:
Glucose molecules are stuck together into chains referred to as glycogen

Glycogen is a great source of energy conveniently stored within muscles.  However, there is a limit to how much glycogen your muscle can hold, and that overflow glucose goes to what everybody does not want- fat:

An example of a triglyceride or fat molecule


So now back to the study.  10 women were followed over a 12 week period.  Half of the subjects consumed 70% of a controlled diet in the AM, while the other half consumed 70% of their controlled diet in the PM.  Halfway through, both groups switched.  This study measured a number of parameters, three of which included body weight changes, fat mass changes, and fat-free mass changes.  This is what they found:
  • More total weight loss was observed in the AM groups 
  • More fat-free weight loss was observed int he AM group
  •  More fat weight loss was observed in the first study period PM group, but not the second

As we may expect, more total weight loss was observed in the AM meal group.  However, interestingly, the PM group showed signs of increased fat loss and preserving lean body mass.

The Importance 

A common way people monitor their weight loss is via the good-old scale.  Consuming more calories during AM meals would appear to help these individuals since weight is the only outcome the scale can measure.  However, weight loss does not equate to fat loss.  With consuming a higher percentage of daily calories at night, lean body mass is more effectively preserved, and more fat is potentially lost.  In other words, you may lose more weight with AM meals, but that is not entirely the weight you want to be losing. 

Why Would this Happen? 

The answer to why we see this trend is unclear based on this study alone.  However, the explanation is undoubtedly rooted in how our food is stored, and how our food is mobilized.

First, take into consideration the AM meal group.  When the subjects ingest food in the morning, it is digested and broken down into glucose, which is then transported to the blood stream.  Then, as these individuals exercise and conduct their daily activities, much of that glucose is utilized before it can be stored.  While this may seem like a positive contributor to weight loss, having that glucose in your stomach also negates the need to mobilize your glycogen and fat stores for energy.  In other words, your fat stays fat because it has no reason to go elsewhere.  

By contrast, take into consideration the PM meal group.  When the subjects ingest the food at night, because less physical activity follows the meal, a higher proportion of the calories are stored (first as glycogen, and then as fat).  This gives the body time to utilize these calories to build and heal the stressed tissues from that day, which theoretically would explain why lean body mass is better preserved in this study group.  In addition, throughout the following day, because fewer calories are consumed at breakfast, the body must tap into the glycogen and fat stores sooner to produce sufficient energy.  Thus, unlike the AM group, the fat does not stay fat as it is mobilized as needed. 

The Basics 

An important note to keep in mind with this study is that no matter which group is considered, all of the women showed decreases in total body weight and fat mass.  The reason for this is two fold; (1) They were all eating a regulated low calorie diet and, (2) They were following a regulated exercise regime.   Essentially, if you are over eating and not taking part in adequate physical activity, these results simply do not apply to you. 


So, is it better to eat a higher proportion of your diet in the morning or at night?  This study strongly suggests that the night time option may be best.  The only catch, I am sorry to say, is this only applies to those who exercise regularly and do not over eat.    


Keim, N.L. et. al. 1996. Weight loss is greater with consumption of large morning meals and fat-free mass is preserved with large evening meals in women on a controlled weight reduction regimen. The Journal of Nutrition. 127: 75-82


1 comment:

  1. nice blog
    thanks for sharing information.
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